Sonar help please

[Tomcat]

A fishing colleague reported that he and his partner caught more than 100 walleye one day jigging the bottom while anchored over depressions on the river bottom in 18 to 30 feet of water. Surprisingly, he also reported that he never marked any fish on his sonar unit while they caught these fish. His sonar unit was a colour unit with 320 vertical pixels and a 20 degree cone angle. Can anyone explain why no fish were depicted on his sonar unit? He also reported that he could easily follow his dropped jig to the bottom on his sonar display. Thanks in advance.

[tonyb]

If his refresh rate was set to the slowest setting, he may have missed fish coming into the cone and taking his jig, then when hooked the current carried the fish out of the cone...

 

Sounds fishy anyway...100 walleye!?

 

Tony

[irishfield]

I just wish I could find a unit that doesn't show fish when they aren't really there....

[BITEME]

I set my refresh around halfway but I still have the same issues lets be realistic some may be paying alot of money but they are not commercial grade

 

whats so hard to believe about 100 walleye......seen it if you land on a school and there feeding it happens

[Bernie]

When fishing for walleye on Nipissing I hardly ever look for the fish on the sonar. I believe they are too close to the bottom for sonar to pick them off. Whenever I seen walleye scuba diving they were on the bottom or very close to it. If I do use sonar for locating walleye its usually when they are feeding on a sandbar.

[BITEME]

When fishing for walleye on Nipissing I hardly ever look for the fish on the sonar. I believe they are too close to the bottom for sonar to pick them off. Whenever I seen walleye scuba diving they were on the bottom or very close to it. If I do use sonar for locating walleye its usually when they are feeding on a sandbar.

 

 

Good Point

[BITEME]

How the heck do you do this quote thing to put it in a nice pretty box

[Terry]

I never really found fish on the sonar in under 30ft of water till I bought the X15

 

I can see fish tight to bottom in 9ft of water....you need to know how to set them up and you need to pay for top of the line units

[tonyb]

How the heck do you do this quote thing to put it in a nice pretty box

 

Like this ^^ ?

 

 

Click the Quote button on the post you want to quote, then click reply.

 

Tony

[keram]

Like this ^^ ?

Click the Quote button on the post you want to quote, then click reply.

 

Tony

 

 

Yup, it still works

[BITEME]

Yup, it still works

 

 

I see

THANK YOU

[Tomcat]

When fishing for walleye on Nipissing I hardly ever look for the fish on the sonar. I believe they are too close to the bottom for sonar to pick them off. Whenever I seen walleye scuba diving they were on the bottom or very close to it. If I do use sonar for locating walleye its usually when they are feeding on a sandbar.

 

Let's consider the worst case scenario in the situation I described (i.e. 30 feet or 360 inches of water). For a sonar unit with 320 vertical pixels, each vertical pixel represents 1.125 inches or 1 1/8 inches. There has to be one pixel between two objects to depict two objects from one another on the sonar screen. To my understanding then, for a sonar unit (with 320 vertical pixels) not to depict a walleye hugging the bottom in 30 feet of water, the walleye would need to be 1 1/8 inch or less in body depth. Consequently, at least from a theoretical perspective, his sonar unit should have been able to depict these bottom hugging keeper walleyes he was catching. In 18 feet of water, the walleyes would have to be even smaller in body depth (2/3 of an inch) not to be detected and depicted on his sonar screen.

 

I'm left wondering whether actual sonar performance just doesn't compare with theoretical sonar performance.

[Bernie]

Being in and around the marine business all my life I fortunately get to try all kinds of stuff. Even the high priced stuff has a hard time to differentiate the walleye from surrounding structure on rocky reefs. So my best catches are when I see no fish at all. On a relatively flat sandbar you look for bumps on the bottom and if you drop a line success will more than likely be had.

[Terry]

a really good sonar will show fish on bottom, it will look like a bump or rock like so many rocks you see on bottom but a good sonar will have a shaded area or grey line between the bump and the bottom

that's a fish sitting there

[Raf]

i think some of you need to turn the fish id off.

[irishfield]

Even with the sensitivity turned down on my LCX112C it's showing way toooo many fish that aren't there. Mind you the built in water temp sensor on my 50/200Hz transducer Lund installed doesn't work on it either and the transducer is being replaced with a new one next week to fix that (or it damn well better)...so hopefully the unit itself has some issues.

 

If I turn fish ID on...there's at least 100 fish on the screen at all times.

[Tomcat]

i think some of you need to turn the fish id off.

 

I dare say most of us turned off Fish ID as soon as we purchased our sonar units. I've been running a Lowrance X-85 for 7 years. I've never ran it with Fish ID on. Regarding fish hugging the bottom, many times, all I've seen is a short thin line, maybe about the thickness of a pencil line, on top of the gray line (bottom). And many times, when I zoomed in 4 X, sure enough, it was a fish.

 

However, I didn't post to argue with anyone. I'd just like a better appreciation of how I should expect a new colour sonar unit with 480 vertical pixels or more to realistically perform. Can the performance of top end sonar units match their theoretical performance?

[Roy]

Tomcat, I put my X-85 at the bow. It still runs like new. It's the best unit I've ever had. The new unit at the back is an LCX-25C. It has 8,000 watts so it's not lacking in power. Here is a screen shot from last Tuesday night. It was zoomed right out and the sensitivity was at its minimum. You can see that there are 4-5 fish on the bottom. I happen to know that they were saugers but this is what it looked like.

 

ps. Had I zoomed in to the bottom, I would have picked up those fish clearly.

[Terry]

I will bet you were trolling Roy

fish show totally different when anchored

[Roy]

Yes Terry...the GPS shows 2mph......was going upstream.

[Terry]

LOL,you are right it does.......

ok I didn't notice

 

 

but when anchored fish on the screen look a lot different

form a long line across the screen to bumps on the bottom or a can show as an uneven bottom changing all the time

[fishnsled]

LOL,you are right it does.......

ok I didn't notice

but when anchored fish on the screen look a lot different

form a long line across the screen to bumps on the bottom or a can show as an uneven bottom changing all the time

 

 

That's the way my unit seems work as well Terry. I've got the fishhawk 480, seems to work very well but a bit slow on the refresh rate. The Lowrance with the extra power and higher resolution does work better, especially when still fishing. imo

[Tomcat]

Thanks for the picture Roy - "worth a thousand words"!!

[duber]

I had the same thing happening last december on the bay . No fish on the Lowrance x97 but caught lots.Next time out I took my Vexlar fl8 flasher and had no problem seeing the fish that were laying right on bottom.

[aplumma]

Their are a few things that are a given as far as the way a sonar unit works

 

The deeper the water and the wider the cone the larger the area is you are reading.

 

The further out from the center of the cone the weaker the return signal is.

 

The return from an object's strength is Dependant on the density of the object.

 

 

 

What you should be thinking when you see a mark on the screen is that mark is the highest point from the signal that is bouncing back to your transducer in the area that the cone is being read. If you have a cone reading a 20 ft radius it is telling you the high spot in that 20 ft circle and no other feature is being returned till the next signal.

 

The cone that is being read is from the center out to the edge of the radius with the center being read the soonest and the strongest.

 

The density compared to the water is how strong a signal bounces off the object. A fish has a density slightly more than water. Mud is denser than fish and rocks/sand is one of the densest materials you will read.

 

 

 

Now look at your color sonar a red return is a very dense return and can be verified as being rocky bottom while a mud bottom has shifted to blue or yellow. Notice at the top of the screen the reflection the wider the reflection the harder the bottom is. Now you can adjust the gain till the rocky bottom gives you a slight return . Now if you are trolling and looking for a fish that likes rocky bottoms you can see at a glance if you are in mud or weeds because the reflection is not at the top of the page. Remember you need to adjust the gain if you vary the depth more than 10 ft or leave the gain turned up and look at the thickness of the return. Now look at the color of the returns that are suspended a yellow blue return that is large in mass and has highlights of red are more than likely bait fish because of the density of the school and the shifting of the red spot areas depths. If you see the same thing and the red spots stay the same and the color patterns dint move then you are reading a ball of weeds or if more red than yellow wood structure that is free floating or possible coming straight up from the bottom.

 

So what does a fish look like color wise is usually blue with a hint of yellow. Since the speed that an object passes thru a cone is what gives the famous arch that some people associate with the size of a fish a slow moving target will look much bigger than it actually is. A good graph to see as you are trolling is a few arches then above them a shifting cloud of yellow and blues with a few arches again below it. Remember you are looking down at the first object the signal strikes so you have found the edge of the predator fish with the arches and the bait scattered by them feeding and then the other side of the fish feeding. By staying over the arches and not over the cloud you will not scatter the bait and still see the fish below.

 

The best thing you can do is to go out in 10 ft of water clear or not and tap a stick on the bottom you will feel the different bottom contours and textures and how they relate to your screen. Think of the return as the highest point of the signal sent that means a rock will hide a fish that is in a depression inside of the cones return. So the long answer to your question is A bottom littered with rubble will often times not show the fish that you are catching that are holding tight to the cover.

 

 

Art